Technical Field
The present invention relates to a motor rotor structure, in particular, to a shaft-embracing permanent magnet inter-shaft glued rotor structure of a high-speed motor.
Description of the Related Art
In order to obtain a smaller rotation inertia and reduce the effects of the centrifugal force on a permanent magnet, high-speed small motors usually adopt permanent magnet structures with a relatively large draw ratio, as shown in FIG. 1. a1 is a rotor shaft; a2 is a permanent magnet; and a3 are balance rings (one on each of the left and right sides).
With such a structure, the permanent magnet is processed with a thin and long hole which is matched with shafts to form a rotary component. Such structure features less components and easy assembly. However, the space proportion of the permanent magnet is small and the shaft segments that adhere to the permanent magnet occupy space, so the space utilization ratio is low.
In order to handle the effects caused by the thin and long holes, a holding structure in which rectangular key grooves are formed at two ends of the permanent magnet are seen in some literatures, as shown in FIG. 2.
Such a structure abandons the idea of matching with the thin and long hole, the permanent magnet and the shaft b1 are connected through a key b2, increasing the space proportion of the permanent magnet. However, the key b2 may have a relatively large offset after assembly, causing the problem of dynamic balance. Stress may be concentrated at the bottom (straight angle) of the rectangular groove b2. When the glue is ineffective, the key b2 loosens and is thrown out, causing a motor failure.
When the permanent magnet is molded by sintering or punching, the permanent magnet may have initial cracks inside. In order to prevent the rotor of the structure as shown in FIG. 2 from breaking from the positions of the cracks during high-speed rotation, the structure form of protecting the permanent magnet with the steel jacket are put forward in some literatures, as shown in FIG. 3.
Such a structure abandons the two-end holding idea and employs a steel jacket c4 to embrace the permanent magnet c3. The steel jacket c4 and the rear shaft c1 are connected at a weld c2. The steel jacket c4 and the output shaft c6 are connected at a weld c5. Such structure ensures the concentricity of the rear shaft and the output shaft through the inner hole of the steel jacket, imposing high requirements on the precision of the inner hole of the steel jacket which results in large process difficulties.